How do you create a moving texture?

[rock3rd]

I am referring to a texture that (in-game) scrolls in a certain direction at a certain speed.

An example of this is in the map Convoy, where the floor beneath the trains scrolls, making it seem like you are moving.

If it is even possible, how do you do it?

 

[theatreTECHIE]

You do it by setting the texture scrolling properties in the vmf. Here's an example from some scrolling clouds I had in my map:

"LightmappedGeneric"
{
    $basetexture "props_vigil/vigil_clouds"
    $translucent 1
    $nocull 1
    $scrollspeed 0.03
    $scrollang 0
  
    $color "[1 0.9 0.8]"
  
    %keywords tf
  
    Proxies
    {  
      
        TextureScroll
        {
            texturescrollvar $basetexturetransform
            texturescrollrate $scrollspeed
            texturescrollangle $scrollang
        }
      
    }
}

The more important part for you is the scrollspeed and scrollang variables, and the Proxies section.